This invention relates to a semiconductor pressure detection device using a semiconductor diffusion resistor having a piezo-effect.
A semiconductor pressure detection device is conventionally used in which a bridge circuit is formed using the diffusion resistors of a semiconductor as pressure-sensitive gauge resistors. Since in such a device the characteristic variation of the gauge resistor with respect to the temperature exerts greater influence to the result of detection, the temperature compensation is conducive to the improvement of a device performance.
FIG. 1 is a circuit diagram showing a conventional semiconductor pressure detection device. Gauge resistors R1, R2 are formed in a surface region of a semiconductor single-crystal substrate and show a resistance variation in a mutually different direction according to pressure applied. A bridge circuit is created by such resistors R1, R2 and pressure-insensitive resistors R3, R4. A constant power source VE is connected to the bridge circuit. The bridge circuit takes a balanced state when no pressure is applied. When pressure is applied, the bridge circuit is put in the off-balance state and a voltage .DELTA.V according to pressure applied is taken out of the bridge circuit. In general, such bridge circuit is such that, when the external temperature varies, output voltage (zero voltage) in the balanced state (when no pressure is applied) varies and at the same time the pressure sensitivity of the gauge resistor varies. If, therefore, a pressure-insensitive resistor RS is connected in series with the gauge resistor R1, a series circuit of the resistors R1 and RS is connected in parallel with a pressure-insensitive resistor RP, and the resistors RS and RP are selected to have proper values, then the apparent temperature coefficient of the gauge resistor R1 is made to approach to that of the resistor R2 within a temperature range used whereby the temperature compensation of the zero voltage is effected. To effect the temperature compensation of the pressure sensitivity it is necessary to vary drive voltage according to the external temperature. A temperature-sensitive resistor element RT such as a thermister is connected in series with the constant power source so as to obtain drive voltage VB according to the temperature. Such a temperature compensation system has the following drawback. Since in this system the zero voltage compensation element and pressure-sensitive compensation element are provided separately from each other, they suffer a different temperature and if drive voltage is varied according to the temperature there arises a problem that a once-compensated zero voltage varies. Particularly where the external temperature is varied rapidly, the zero voltage could not be adjusted according to the drive voltage, producing a compensation error. Further, since the pressure-insensitive resistor is connected in parallel with the gauge resistor the linearity of the pressure-sensitive characteristic of the gauge resistor is deteriorated, impairing a measuring accuracy.